1. Field of the Invention
The invention generally relates to a method for blow molding a container, and more particularly to a method for blow molding a container to be formed with deep-set grips so that the formed container has secure grippability along with a good ergonomic feel.
2. Related Art
One method of manufacturing containers is through a process known as stretch blow molding. In this process, a preformed parison, or preform, is prepared from a thermoplastic material, typically by an injection molding process. The preform typically includes a threaded end, which becomes the threads of the container. During stretch blow molding, the preform is positioned between two open blow mold halves. The blow mold halves close about the preform and cooperate to provide a cavity into which the preform is blown to form the container. Once the mold is closed, a gas is forced into the perform causing it to stretch and to take the shape of the mold as the plastic contacts the mold. After molding, the mold halves open to release the blow molded container.
One problem with stretch blow molding is that stretching of the plastic material may affect the performance of the container at certain areas. While the stretching of the plastic material may not cause problems for most sections of the container, it particularly affects the ability of the plastic material to form around a deep protrusion in the mold. In some applications of container manufacturing, a deep protrusion may be required to form a particular section of a container. For example, the particular sections of the container formed by an inset or deep protrusion may include the dome, sidewalls, and the base of the container. As the plastic contacts the deep protrusion of the mold, the plastic must stretch and flow around the protrusion into a recess. However, the plastic material is less able to flow and stretch around the protrusion because of the contact friction with the mold surface. Insufficient material distribution at a region, such as at the base, may affect the ability of the region to maintain its shape around the protrusion during hot filling, the strength of the region, or the ability of the container to stand on a flat surface.
A lack of definition in the base caused by the inability of the plastic to properly form at a deep protrusion is a particular problem. While this is a particular problem in the base region, similar problems exist in other regions of a container where an inset is positioned. As stated previously, these other regions formed with an inset or deep protrusion include the dome, the sidewalls, etc. of a container. These problems can exist with any forming process, such as blow molding, where material must flow around a protrusion of a mold to form an inset region of a container. This is particularly true for blow molding processes including stretch blow molding, extrusion blow molding and injection blow molding.
Some containers have deep-set grips on either side of the bottle so that a consumer can easily pick up the filled container with a firm grasp of his/her hand. When blowing deep-set grips with known blow molding processes, plastic material becomes trapped in the grip regions consequently starving other regions of the container of material. To account for this, the container weight is increased as more material is required to be used to ensure that a sufficient amount of material is provided for all parts of the container. Alternatively, design compromises are made so that the resultant thinner regions are closer to the axis of the container causing those regions to be blown with more material. However, blowing heavier containers and the resultant design constraints do not solve the problem described above.
What is needed is an improved method of forming a container with a deep-set protrusion (e.g., in the base and/or as a grip) that overcomes the shortcomings of conventional solutions that introduce additional costs, molding time, and complexity into the mold setup.